1. Field of the Invention
The present invention relates to a method and apparatus for transmitting information about an electronic device employed as a primary information signal receiver device to an electronic device employed as a primary information signal sender device in a system in which a primary information signal such as a video signal or an audio signal is transmitted to the sender device to the receiver device. More particularly, the present invention relates to an information signal transmission method, an information signal transmission system, an information signal transmitting apparatus used in the system, an information signal receiving apparatus used in the system, and methods for information signal transmitting apparatus or receiving apparatus to transmit or receive an information signal, which allow device information to be transmitted.
2. Description of the Related Art
Various digital contents are provided via broadcast media such as digital broadcasting, communication media such as the Internet, or a recording medium such as a CD (compact disc), an MD (mini disc), or a DVD (digital video disc). However, a great problem is that digital contents are often copied illegally by unauthorized users. Thus, there is a need for a reliable technique of protecting copyright of digital contents.
To prevent the above problem, it is known in the art to supply a digital content together with information for managing its copying (copy management information) attached thereto such that a copying operation performed by a recording apparatus or the like is controlled in accordance with the copy management information attached to the digital content thereby preventing the digital content from being copied illegally.
However, even when copy management information is attached to a digital content, it is impossible to correctly control the copying operation in accordance with the copy management information unless a recording device or the like has the capability of performing a copying operation in accordance with the copy management information (that is, unless the recording device used is compliant). In other words, even if copy management information is attached to a digital content, it is possible to illegally copy it using a device (noncompliant device) which does not have the capability of controlling the copying operation in accordance with copying management information.
One known technique for protecting copyright of a digital content in a more reliable fashion is to use an IEEE1394 digital interface. When two electronic devices are connected to each other via an IEEE1394 digital interface, if an electronic device employed as a digital content receiver device is a compliant device, device information associated with the receiver device is transmitted to an electronic device employed as a digital content sender device.
For example, when a device which receives a digital broadcasting signal and outputs the received signal is employed as the digital content sender device and a compliant recording device is employed as the digital content receiver device, information indicating that the receiver device is a recording device is transmitted from the receiver device to the sender device via the digital interface.
The digital content sender device outputs a digital content to the digital content receiver device after encrypting the digital content. Furthermore, on the basis of information returned from the receiver device via the digital interface, the sender device determines whether the receiver device is compliant. The sender device also checks copy management information attached to the digital content and determines whether a key used to decrypt the digital content should be sent to the receiver device, depending upon the copy management information and also depending upon whether the receiver device is compliant.
More specifically, when the receiver device is a compliant device, the key required for decryption is sent to the receiver device. However, the key required for decryption is not sent if the receiver device is noncompliant thereby effectively preventing the digital content from being illegally copied. Such a communication control technique is called an IEEE1394 secure bus.
In some cases, a digital content is converted to an analog signal, and the resultant analog signal is supplied to a conventional VTR (video tape recorder) or cassette tape recorder and recorded on a video tape or a cassette tape. However, conventional analog electronic devices such as a VTR and a cassette tape recorder have an analog input terminal which accepts only an analog video signal or an analog audio signal.
Therefore, when an electronic device such as a digital broadcast receiver or a digital content reproduction device converts a digital content into an analog signal and outputs the resultant analog signal together with copy management information, it is impossible to protect copyright of the content because the primary information signal sender device cannot know whether an analog electronic device employed as the primary information signal receiver device is a compliant device having the capability of performing a copying operation in accordance with the copy management information, unlike the system using the above-described digital interface which ensures protection of copyright.
One possible method for avoiding the above problem in a system using an analog interface is to transmit device information associated with an electronic device employed as a primary analog signal receiver device from the primary analog signal receiver device to an electronic device employed as a primary analog signal sender device, in a similar manner as with the IEEE1394 digital interface described above, thereby making it possible for the primary analog signal sender device to control outputting of a primary analog signal taking into account also the device information associated with the primary analog receiver device.
However, in order to send the device information associated with the primary analog signal receiver device to the primary analog signal receiver device, it is required to provide an additional transmission line via which the device information is transmitted. More specifically, it is required that the primary analog signal receiver device should have an additional output terminal for outputting the device information and the primary analog signal sender device should have an additional input terminal for inputting the device information, and it is required that these input and output terminals are connected to each other via a cable. An alternative method for sending the device information is to use wireless transmission.
The additional cable transmission line or wireless transmission line for transmitting the device information results in an increase in the production cost of the electronic device used as the primary analog signal sender or receiver device. Furthermore, even in a system designed to use an additional transmission line to transmit device information, it is impossible to protect copyright of a content if a user does not correctly connect the additional transmission line to sender and receiver devices. That is, there is a possibility that the additional transmission line becomes useless.
In view of the above, it is an object to solve the above problems. More specifically, it is an object of the present invention to provide an information signal transmission method, an information signal transmission system, an information signal sending apparatus, an information signal sending method, an information signal receiving apparatus, and an information signal receiving method, which allow information about a primary information signal receiving device to be reliably supplied to a primary information signal sending device via an existing analog transmission line or digital serial transmission line.